The overall goal for this project is to forge a series of links between transepithelial transport processes and the individual membrane mechanisms (apical and/or basolateral) that help regulate the chemical composition of the intracellular milieu. In order to study this relationship we will use tracer flux techniques to determine the magnitude and direction of active ion transport across the pigment epithelium (PE). We will use conventional and ion-selective microelectrodes to determine the driving forces for passive and active (or carrier mediated) transport processes. Fluid transport will also be measured and we will determine which active transport mechanisms are osmotically coupled to fluid flow. Fluorescence techniques will be used to measure intracellular pH and Ca. One of the important goals of this project is to test the fundamental hypothesis that mechanisms which play an important role in regulating intracellular pH and Ca also regulate transepithelial ion and fluid transport and the chemical milieu of the subretinal and choroidal spaces. The electrooculogram (EOG) is a light evoked change in standing potential across the human eye and is produced by a depolarization of the RPE basolateral membrane. The clinical evaluation of PE disease might be improved if we knew which membrane mechanisms were responsible for the EOG light peak. Similarly, we could gain a much deeper understanding of retinal detachments if we know which membrane mechanisms are responsible for fluid transport across the RPE. It will be important to examine the adhesivity between pigment epithelium and retina as a function of PE fluid transport rate. If intracellular pH regulation played a key role in phagocytosis and disc shedding, or in controlling the esteryfing enzymes in the vitamin A cycle, it could be important for understanding RPE pathogenesis.